956
UNIT 4
Maintenance of the Body
25
hydronephrosis
(hi
0
dro-nĕ-fro
9
sis; “water in the kidney”). Hy-
dronephrosis can severely damage the kidney, leading to necro-
sis (tissue death) and renal failure.
Internal Gross Anatomy
A frontal section through a kidney reveals three distinct regions:
cortex
,
medulla
, and
pelvis
(Figure 25.3)
. Te most superficial
region, the
renal
cortex
, is light-colored and has a granular ap-
pearance. Deep to the cortex is the darker, reddish-brown
re-
nal
medulla
, which exhibits cone-shaped tissue masses called
medullary
or
renal pyramids
. Te broad
base
of each pyra-
mid faces toward the cortex, and its apex, or
papilla
(“nipple”),
points internally. Te pyramids appear striped because they are
formed almost entirely of parallel bundles of microscopic urine-
collecting tubules and capillaries. Te
renal columns
, inward
extensions of cortical tissue, separate the pyramids. Each pyra-
mid and its surrounding cortical tissue constitutes one of ap-
proximately eight
lobes
of a kidney.
Te
renal
pelvis
, a funnel-shaped tube, is continuous with
the ureter leaving the hilum. Branching extensions of the pelvis
form two or three
major
calyces
(ka
9
lih-sēz; singular: calyx).
Each major calyx subdivides to form several
minor calyces
,
cup-shaped areas that enclose the papillae.
Te calyces collect urine, which drains continuously from
the papillae, and empty it into the renal pelvis. Te urine then
flows through the renal pelvis and into the ureter, which moves
it to the bladder to be stored. Te walls of the calyces, pelvis,
and ureter contain smooth muscle that contracts rhythmically
to propel urine by peristalsis.
Homeostatic Imbalance
25.2
Pyelitis
(pi
0
ĕ-li
9
tis) is an infection of the renal pelvis and caly-
ces. Infections or inflammations that affect the entire kidney are
pyelonephritis
(pi
0
ĕ-lo-nĕ-fri
9
tis). Kidney infections in females
are usually caused by fecal bacteria that spread from the anal re-
gion to the urinary tract. Less oFen they result from bloodborne
Body wall
Perirenal
fat capsule
Renal
artery
Renal
vein
Inferior
vena cava
Aorta
Fibrous
capsule
anterior
posterior
Renal fascia
Supportive
tissue layers
Body of
vertebra L
2
Peritoneum
Peritoneal cavity
(organs removed)
Anterior
Posterior
12th rib
(b)
(a)
Figure 25.2
Position of the kidneys against the posterior
body wall.
(a)
Cross section viewed from inferior direction. Note
the retroperitoneal position and the supportive tissue layers of the
kidney.
(b)
Posterior in situ view showing relationship of the kidneys
to the 12th ribs.
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